Replacing plywood roof deck


#1

My cheap roof has 3/8" plywood 30 years old. I’m replacing the “bad” stuff with 7/16" OSB. Question is how bad is bad and nailing the new stuff by hand is a real pain and time consuming. Any reason I can’t use my roofing nailer to nail down the new sheathing? The old plywood appears dried out, but as long as it isn’t cracked do I really need to replace it?


#2

So you are replacing cheap thin 3/8" plywood with the cheaper version of OSB rather than spending a few dollars more per sheet to make it last, by using a thicker panel? Why?

Roofing nails are only 1 3/4" maximum in length.

You need to use 8 penny nails, spaced 6" OC on the perimeter edged and 12" OC on the interior rafters.

Ed


#3

I went with 7/16" osb to match closer to the 3/8" rather than use 1/2" and cause a rideg. I’m okay using 1/2", provided it blends okay with 3/8" existing in case I don’t replace it all. I asked the roofing supplier and they said 7/16" is typical, anything more is overkill. Thanks for the advice on nailing, I have been using 8 penny, just thought I might speed things up a bit. I’m a one man show and I have about 14 square to replace. Takes about 25 min to replace a 4x8 sheet hand nailing.


#4

Hi,

The length of the nail is not the main issue. Roofing nails the heads will pop off. They are not meant for the stress of holding wood together.


#5

OSB is certified CRAP. use CDX plywood.


#6

[quote=“ed the roofer”]So you are replacing cheap thin 3/8" plywood with the cheaper version of OSB rather than spending a few dollars more per sheet to make it last, by using a thicker panel? Why?

Roofing nails are only 1 3/4" maximum in length.

You need to use 8 penny nails, spaced 6" OC on the perimeter edged and 12" OC on the interior rafters.

Ed[/quote]

chickenhawk, I would just replace it all. Even the 3/8" of mine that’s still “good” is still crap.
Ed, I’m in the same boat with soft 3/8" Ply on a 14 Sq roof. One estimator said 1/2" CDX anything more was a waste. The other said 5/8" CDX or 3/4". 3/4 just seems too thick and heavy. I think I am settling on 5/8" Is tongue and groove better than square edge with clips? Are regular 8 penny nails fine or ring shank better?


#7

[quote=“mjzraz”]

[quote=“ed the roofer”]So you are replacing cheap thin 3/8" plywood with the cheaper version of OSB rather than spending a few dollars more per sheet to make it last, by using a thicker panel? Why?

Roofing nails are only 1 3/4" maximum in length.

You need to use 8 penny nails, spaced 6" OC on the perimeter edged and 12" OC on the interior rafters.

Ed[/quote]

chickenhawk, I would just replace it all. Even the 3/8" of mine that’s still “good” is still crap.
Ed, I’m in the same boat with soft 3/8" Ply on a 14 Sq roof. One estimator said 1/2" CDX anything more was a waste. The other said 5/8" CDX or 3/4". 3/4 just seems too thick and heavy. I think I am settling on 5/8"

**Is tongue and groove better than square edge with clips? **

Are regular 8 penny nails fine or ring shank better?[/quote]

Tongue and groove is going to real overkill for the additional price, especially if you do use the 5/8" CDX sheathing.

Those annular shanked nails are a real “Mother” to pull back out. They are great for pull-out resistance though and do not cost much more than smooth shank. especially if you or your contractor is using a coiled framing gun.

The air setting has to be adjusted a bit higher to make sure they sink in all the way though, otherwise the roofer/carpenter is going to be pulling out his framing hammer quite a few times if he is conscientious.


#8

just remember roof decks are not dance floors.
they are there to hold the roof up and on.

gweedo.


#9

I am keeping this in the same thread since I think it’s still on the topic of replacing plywood.

I got material costs (in MD) for roof decking (14 Sq @40 pcs)
7/16 OSB - $9.26 each = $370
1/2" CDX 4 ply - $16.95 each = $678
5/8" CDX 4 ply - $21.57 each = $863

Ever heard of Advantech Sheathing by Huber?
50 yr warranty and supposed to be more stable etc:
huberwood.com/main.aspx?pagename … hsheathing

I found a supplier going out of business that has the 1/2" for $10 a sheet. Is this just OSB with “perfume” sprayed on it?


#10

Advantek is more of a sub-flooring product, and it holds up to quite a bit of wet/dry cycling without swelling or cupping. I know this from past Framing experience, over 300 homes, and Advantek is the best when it comes to Sheething… also I want to post some pics to show what I am finding on the tear offs that I am doing to show the difference between osb and REAL plywood, the REAL plywood is a mess and the nails are coming through the shingles from the REAL plywood walking of the roof on its own… I have found that O.S.B. has held up to the test of time and if installed properly will hold up for the next guy after me! All I do is see what is in front of me, and all I see when I tear off the shingles and paper is REAL plywood beging to be replaced W/ O. S. B. ! (IMO)


#11

Thanks…my next question was why are there so many bad comments about OSB? The last response was more in line with what I’ve heard about OSB, I thought it was actually a preferred material for roofing…at half the price. In any case, I’m already using it. Thanks for all the comments, great help for the do it yourselfer.


#12

They have Sheathing and flooring, but I am not sure the difference other than the rating. They supplier said he has “Advantech 40C in 1/2” " I can’t find what 40C is.
Also I still can’t find much info on Advantech vs “regular” OSB.

I would like to see those… Are the roofing nails backing out or the nails holding the sheathing to the framing backing out?


#13

The sheething nails are being puled out as the plywood ages and dries out I supose. I have not seen this with osb. The only problem is with osb you must install smooth side down and sometimes it is not installed properly so the moisture from the attic does affect it as far as softening between rafters, but it still holds the fasteners, and also has a good density, like when you beat on it with a hammer it sounds sollid…not like plywood that has been affected by moisture and dryrots and delaminates and your hammer goes right through…I will try to get these pics uploaded today. I have tons …Probably more than most REAL Plywood lovers want to see…lol (IMO).lol ,.Years ago I felt the same about PRESSED board, but they have some great strides forward in the ENGEINERED wood department. Advantek and osb ratings are numbered by GLUE content and Anvantek is very dence and will outlast any sub-floor product for wet dry cycling…(IMO)I was framing a 6400 square house for a high end builder and was there about 1 month with small crew in the end of winter begining of spring ,so I saw first hand how it stands up to wet/dry affects…That was at the end of my framing days about 5 yrs ago .


#14

I have noticed the same thing that Jwolf has.
OSB is perfectly good for roof sheathing, you should use a min of 1/2" though.
Plywood delaminates a lot, and if it gets wet it warps.
There also seems to be more sheathing nails backing out with plywood.
OSB has a paraffin coating on it that protects it from moisture.
Plywood does hold nails better and is a better choice for thinner sheeting and 24" o.c spans.
When replacing bad sheeting it is best to replace it with what is there.

IMO 7/16" OSB is too thin for roof sheathing, were as 7/16" plywood is adequate.


#15

Axiom said 7/16 plywood , but plywood comes 3/8,1/2,or5/8,3/4 , not 7/16 possably 19/32 ,but not 7/16,or is that a MICH. thing…lol


#16

1/2" nominal thickness plywood is actually 15/32’s.

Have you ever torn of any OSB that has been on a roof for 40 plus years?

Of course not. It hasn;t been around that long.

Ed


#17

Obviously not…but I have not ripped of a roof that had O.S.B. that was completely wasted and every sheet needed to be replaced as with so many roofs with plywood…same age or younger…sorry but that is the facts as I see it over and over again…I to used to feel that Plywood was the best, when I was much younger, and also felt that Wood Siding was all I would ever install, but times they are a changin, and advancements are being made in newer and far superior products,every day…they now have osb with a coating that you need no paper ,just tape the seams and leave in weather for up to 60 days,I don’t see where it is cost effective to use this since I have no need to leave a job exposed for any length of time…For example just walk into Home Depot, and look at the stacks of plywood, and osb, need I say more about which product must lay flatter when nailed to rafters…I am sure we could go back and forth at this for ever…I was just like you…and now I see more and am open to try new things…


#18

You might check the building code in your area. Most codes will not allow the use of 3/8" plywood for roofing underlayment.

Bottom line, thicker is better. OSB can be good and bad. There is a significant quality difference in various brands. I do fastener pull tests all the time on decking and see quite a difference in brands. When in doubt, go to 5/8" (or fractional thickness) OSB to get the best job and the highest pull out strength. Better yet, use 1/2" or better plywood.


#19

I agree completely with Don.

As a matter of fact, I have posted the Fastener Pull Out Test results on this forum previously. If I can find that post, I will copy/paste the results here later tonight.

Ed


#20

I’m not against OSB, it fills the need for cheaper and cheaper underlayment. That is why Home Depot has big stacks of it. Do be aware that there are lots of different brands of OSB and not all of them are good. In the same light, there are lots of bad plywood brands. I would venture a guess that the stuff you pulled off was not 5 ply or better and had been wet or damaged. Get OSB wet in the same way and see how it comes off.